The present invention relates to the storage and retrieval of information from optical media and pertains particularly to an improved high bandwidth focus actuator and suspension system for use in an optical disk drive.
Optical disk drives are in widespread use and include video disk drives used in video applications as well as optical disk drives that serve as a peripheral memory storage devices in computer systems. The latter category includes write-once-read-mostly (WORM) drives, CD-ROM drives and magneto-optic (erasable) drives.
In one form of optical media, information is encoded in concentric or spiral tracks on the surface of a disk by physically altering minute regions of the media to change the reflectivity thereof. Data is written and read from the optical media utilizing a laser beam which is reflected off of the media. It is critical to maintain the laser beam in focus at the appropriate level of the optical media.
Optical focusing systems are well known for this purpose and typically include an optical head having an adjustable objective lens to allow focusing of a laser beam onto a storage media. Typically the lens is directly driven by an electromagnetic motor such as a voice coil motor (VCM). The lens is usually mounted on a movable portion of the motor. The suspension of the lens mount is critical and must allow for very precise vertical movement.
For some applications, it is desirable to have an objective lens move only in the axial direction to maintain focus and not move in other directions. It is also highly desirable for the structure to have minimum resonances.
One frequently used approach is a plain bearing constraint and a moving VCM. However, hardware using this approach may suffer from wear and stick slip induced non-repeatability of motion. Adequate constraint of tilt and lateral motion is difficult.
Another approach uses a moving magnet for generating the force and a cantilever arrangement which allows for horizontal displacement. Such a system is disclosed in U.S. Pat. No. 4,633,456.
The prior art systems have a number of drawbacks including low efficiency and inadequate bandwidth. Another drawback is lack of adequate constraint against lateral motion and tilt. It is therefore desirable that an improved suspension system and high performance actuator be available for use in the optical head of an optical disk drive system.